The previous four pages — Resource, Exporter, Span Processor, and Tracer Provider — walked through the OpenTelemetry tracing components one by one. Wiring them up by hand in every application is verbose. The phoenix.otel SDK collapses all of it into a single function call — and adds a few Phoenix-specific capabilities on top. For the practical how-to of installing and using these helpers, see Set up tracing. This page covers what they do under the hood.

Appreciate the Simplicity

Configuring tracing with raw OpenTelemetry — Resource, Exporter, Span Processor, Tracer Provider — looks like this:

from opentelemetry import trace
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import BatchSpanProcessor
from opentelemetry.sdk.resources import Resource
from opentelemetry.exporter.otlp.proto.http.trace_exporter import OTLPSpanExporter

def init_phoenix_tracing():
    resource = Resource.create({
        "openinference.project.name": "my-project",
    })
    otlp_exporter = OTLPSpanExporter(
        endpoint="http://localhost:6006/v1/traces",
    )
    span_processor = BatchSpanProcessor(otlp_exporter)

    tracer_provider = TracerProvider(resource=resource)
    tracer_provider.add_span_processor(span_processor)
    trace.set_tracer_provider(tracer_provider)

    return tracer_provider.get_tracer("my-project")

The Phoenix register() helper replaces all of that:

from phoenix.otel import register

tracer_provider = register(project_name="my-project")

Same outcome — Resource, Exporter, Span Processor, Tracer Provider all wired up — in much less code.

What `register()` Does Under the Hood

The convenience function handles four things for you. Each one has additional capabilities specific to OpenInference and Phoenix compared to the standard OTel SDK:

Component returned by `register()`	What it adds beyond standard OTel
Tracer Provider	A Phoenix-aware provider with sensible defaults. Combined with the OpenInference instrumentation libraries, it makes the OpenInference context managers (`using_session`, `using_user`, `using_metadata`, etc.) attach attributes to spans automatically.
Span Processor	Configured and pre-attached. `SimpleSpanProcessor` by default, `BatchSpanProcessor` when you pass `batch=True`.
Span Exporter	Auto-detects gRPC or HTTP from the endpoint URL and configures the matching OTLP exporter. If `api_key` is set, it adds the `Authorization: Bearer <key>` header for you.
Resource	Sets the project name automatically from your `project_name` argument (or the `PHOENIX_PROJECT` environment variable, with `PHOENIX_PROJECT_NAME` accepted as an alias).

Auto-instrumentation

register() has an auto_instrument=True option that automatically calls .instrument() on every OpenInference auto-instrumentor installed in your environment.

from phoenix.otel import register

tracer_provider = register(
    project_name="my-project",
    auto_instrument=True,
)

That single call replaces manually doing OpenAIInstrumentor().instrument(...), LangChainInstrumentor().instrument(...), and so on for every installed instrumentor. Just pip install the instrumentors you want active, and auto_instrument=True finds them at runtime. For the full set of installable instrumentors, see the OpenInference repository.

Configuration

register() reads from environment variables when arguments aren’t passed:

Argument	Environment variable	Notes
`project_name`	`PHOENIX_PROJECT` (alias `PHOENIX_PROJECT_NAME`)	Name of the project in Phoenix. If both env vars are set, `PHOENIX_PROJECT` wins. Defaults to `"default"`.
`endpoint`	`PHOENIX_COLLECTOR_ENDPOINT`	The collector endpoint. Defaults to `http://localhost:6006`.
`api_key`	`PHOENIX_API_KEY`	Optional for local Phoenix. Required for Phoenix Cloud or any authenticated instance — added as a Bearer token header.
`headers`	`PHOENIX_CLIENT_HEADERS`	Additional headers for the OTLP request (e.g. tenant identifiers).

The full signature:

register(
    *,
    endpoint: Optional[str] = None,
    project_name: Optional[str] = None,
    batch: bool = False,
    set_global_tracer_provider: bool = True,
    headers: Optional[Dict[str, str]] = None,
    protocol: Optional[Literal["http/protobuf", "grpc"]] = None,
    verbose: bool = True,
    auto_instrument: bool = False,
    api_key: Optional[str] = None,
)

All arguments are keyword-only.

Multi-project routing

Phoenix is typically deployed as one instance per environment, and each application sends all of its traces to a single project. If you need to route traces from one application to multiple projects, the options are:

Multiple register() calls with different project_name values and set_global_tracer_provider=False on all but one. You then have to track which tracer provider to use where in your code.
OpenTelemetry Collector with a routing connector — let the application send all spans to the Collector, then route to different Phoenix projects (or different backends entirely) based on span attributes. See OpenTelemetry Collector.

For the common case — single app, single project — one register() call is everything you need.

When to Use Which

Use case	Recommended approach
Single project, simple app	`register(...)`
Single project + auto-instrument every installed library	`register(project_name=..., auto_instrument=True)`
Multiple projects from one app	Multiple `register()` calls, or an OTel Collector routing connector
Maximum control, custom processor pipeline	Raw OTel — see Tracer Provider

Next step

You’ve covered every component on the OTel side. Time to learn what OpenInference adds on top — starting with the semantic conventions that make AI traces meaningful:

Get Started

MCP

Tracing

Evaluation

Datasets & Experiments

Prompts

Settings

Concepts

Resources

The phoenix.otel Helpers

Appreciate the Simplicity

What `register()` Does Under the Hood

Auto-instrumentation

Configuration

Multi-project routing

When to Use Which

Next step

Next: OpenInference Semantic Conventions

​Appreciate the Simplicity

​What register() Does Under the Hood

​Auto-instrumentation

​Configuration

​Multi-project routing

​When to Use Which

​Next step

Next: OpenInference Semantic Conventions

Appreciate the Simplicity

What `register()` Does Under the Hood

Auto-instrumentation

Configuration

Multi-project routing

When to Use Which

Next step